Optical Control of Plasmonic Ferritin Based Quantum-Biological System

Ferritin protein is a self-assembled nanocage consisting of 24 subunits that have documented quantum dot material properties and can enable quantum mechanical electron transport over substantial distances. Ferritin is abundant in the dopamine neurons of the substantia nigra pars compacta and the norepinephrine neurons of the locus coeruleus. The distinct organization of neuron subgroups with extensive axon branches and synapses may have evolved to utilize electron transport mechanisms for coordinating conscious actions or other functions. Optically controlled charge transport in direct or indirect bandgap semiconducting ferritin protein quantum structures could enhance electron transfer mechanisms between neurons. This electron transport might be augmented by ferritin present in the intercellular fluid between neurons, alongside the creation of internal cell voltages and pressures.<br/>In this work, apoferritin layers with a tunable bandgap tailored by the number of monolayers have been coupled to biocompatible Au nanoclusters or carbon quantum dots. The quantized states within the ferritin protein layer have absorption states above 4 eV, and its electron transport mechanism due to ultraviolet light excitation has never been studied before. The fluorescence properties of the ferritin protein with peak emission at 325 nm can be enhanced and modified by the inclusion of the Au nanocluster in and around the self-assembled protein nanocages. The emission lifetime of the protein is reduced from 1.5 microseconds to 4.14 ns due to the efficient charge transfer. Carbon quantum dots with emission in the UV wavelength can also enhance the fluorescence properties of the protein due to the Förster resonant energy transfer mechanism. Nondegenerate differential transmission spectroscopy has also been performed to study the light scattering mechanism in the apoferritin layers coupled to the Au nanoclusters. The differential absorption rate of the quantum states within the apoferritin layer is significantly enhanced due to coupling with the Au nanoclusters, and the carrier lifetime is observed to be 15 ps. The UV absorption peak is usually not efficiently observed in the absence of the Au nanoclusters. The efficient charge transfer facilitated by the Au-nanoclusters enables the observation of the higher energy states within the quantized protein layer.<br/><br/><br/>The efficiency of the optically enhanced charge transport process within the Au-nanocluster coupled Ferritin layer has been verified using a solid-state device. A three-terminal device was fabricated using the Au-cluster coupled ferritin layer. The change in the electrical transport characteristics was measured using photocurrent spectroscopy. The photocurrent due to the Au nanoclusters is enhanced from a nano-amp scale to microampere scales due to UV light excitation. The electronic charge transfer can be controlled by the wavelength and photon density of the excitation source.<br/>This novel apoferritin-based synthetic quantum biological protein cluster is an intrinsic semiconductor. The structural analysis supported by the optical and electrical properties of the clusters doped with Au nanocrystals suggests that it behaves like a doped semiconductor. The electron transport and photoelectric response performance can be enhanced by orders of magnitude. It provides a unique pathway to control and manipulate neural activity by modifying the excitation of the quantum states selected by optically tunable radiation.